I have a few bottles of paint (both enamel and water) that most of the thinner has evaperated from (why does this happen more on bottles than tins, but bottles close easier?). What’s the best stuff to rethin them with? (I normally only use turps, metho or water for clean up, or thinning for my airbrush)
This could be tricky-I would use the type of thinner recomended for the paint by the manufacture. Example would be Testors Model master paints recomend using their air-brush thinner for thinning-NOT common thinners such as mineral spirits. This would apply to thickened paints, not to ones that are nearly dry. The other problem is that often as paint begins to dry, it cures. In other words, the molecules actually link together to form a solid surface. Even if you thin them back out, there may be clumps or flakes that will clog your airbrush or show up when you brush. Straining it is a must! Sometimes, though it may be expensive, it may time to call a bottle of paint a loss…
If the paint’s gone off, well… it’s gone off.
I would be thinking about replacing it rather than trying to resurrect it. Compared to the cost of a new model these days, paint is cheap. It’s arguably the cheapest part of the system, but it’s the paint job that makes or breaks a project.
It’s far easier to buy new paint than it is to strip a paint job gone bad. It’s also cheaper than buying a new kit.
However, if you absolutely must try, use the manufacturer’s own dedicated thinner, add small amounts at a time and stir well. If you encounter any lumps or strings of paint which won’t go away no matter how much you stir, toss it and buy new paint.
If you do successfully “restore” it, test on an old junker first before committing to a “live” build. Also, be prepared to use it all up ASAP, no more than 2 weeks at the outside.
I’ve even had paints that look and smell “off” after a while-you wouldn’t think paint could spoil like milk, but it does. I had a bottle of MM paint I tried to resserect, but no matter how I mixed and thinned, it would not spray well. I even ran it through a fine strainer and that didn’t help. My biggest problem was that I was away from the hobby for about 10 years and when I returned I lost quite a bit of my paint inventory. I have to agree with with Phil_H here. One way to minimize the expense of replacing them is to buy only what you know you need-not for future projects. I had so many colors of paint I tossed that I never used because I bought them “just in case” I found a project to do.
Thanks for the replys guys. All the paint is still mostley fine, just very thinck with a small layer of thinner of the top. I’ve had success before with acrylic and methylated spirits/pure alchohol, but have never tried with enamel paints. I figured with methylated spirits, not expensive no loss if it doesnt work, but with enamel i figured I may need a thinner as expensive a new bottle of paint. Thanks again
Andrew
I’ve had paints which simply looked thickened due to thinner loss. When “reconstituted” to a paintable consistency, they’ve been little more than particles of cured/semi-cured paint suspended in thinner. Little to no adhesion, no coverage, gritty finish.
I’m sure you get the picture.
Be warned.
First off, heed Phil’s advice! All of it!
Second, the thinner you use must be the brand’s proprietary thinner unless you are a paint technologist who really knows what they’re doing.
And don’t bother trying this with a metallic paint of any kind. Just replace it. It is a given that the metallic pigment has clumped beyond repair. Metallics are not, and cannot be made, to be as long term stable as other colors. (Some lacquers are exceptions, like Alclad, but they are true lacquers—whole different can of worms…
From the OP’s description of the paint, I would say replace it. I have dealt with it many times and its just too hard to get it to a pure liquid again, and its especially hard to get the lumps out which can clog and airbrush or ruin a finish. I would clean out the bottles and use them for mixing 
I agree with Phil 110% Paint is not that expensive people. [:)]
FWIW, I just “fixed” a bottle of Tamiya flat red acrylic (XF-7, I believe). It was a big gloppy mess with some thinner on the surface. So, I took my electric stirrer and slowly worked in some Tamiya thinner (X-20A). After a few minutes, the consistency look comparable to a fresh bottle and it sprayed just fine.
It can be done, but sometimes, it’s just easier to replace the bottle.
-Fred
Tamiya Acrylics seem to have no problem (except for their metallics), and I have bottles that are at least 25 yrs old that works fine.
Enamel paints are a totally different matter and I have seen Testors Enamel congeal within two years into a rubbery mass.
Store them upside down so that the thinner stays away from the cap where it can evaporate.
Acrylics, Model Master Acryl and Tamiya will re-thin just fine with Tamiya Acrylic thinner. I had a bottle of Model Master flat black that had turned into an extremely thick blob of goo, and after mixing in Tamiya thinner, it was good as new.
As for enamels, Model Master brand is what I use, don’t bother. I’ve never been able to really rescue a bottle of it.
Andy